Magnetic disk drive using a nonvolatile solid state memory to store defect information

ABSTRACT

A magnetic head drive of the present invention comprises a composite magnetic head structured by integrally combining a write head into a record head and a magnetic disk having a servo area where position information of the composite magnetic head is recorded and a data area where data is recorded, and the servo area includes a positioning data area having head positioning information, and the head has an erased area generated by recording an AC signal having a frequency higher than a burst pattern in an area other than the burst pattern including information of positioning the composite magnetic head of said positioning data area.

This application is a Continuation of application Ser. No. 08/299,667,filed on Sep. 2, 1994, now U.S. Pat. No. 5,786,957.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a disk drive such as a hard disk driveand a floppy disk drive using mainly a composite magnetic head with athin film type wherein a write head and a read head are structured in acomposite form.

2. Description of the Related Art

In the conventional magnetic disk drive, there is a disadvantage inwhich the performance of the recording and that of the reproducingcannot be suitably designed since recording and reproducing of signalsare performed by the same head even if an access system of the headdiffers. As a technique for solving this problem, there is known amethod for making the recording and the reproducing suitableindependently by structuring the write head and the read head in acomposite form. This type of the head is called as a composite head todistinguish from the conventional recording/reproducing common head.

A head which a magnetic force generating coil is combined into aring-shaped core, which is designed such that a suitable signalrecording can be performed as a recording head, is used (hereinaftercalled as an inductive head for convenience based on a reproducingprinciple through it is not suitable for a name of the write head).Also, an inductive head or a magnetoresistive head (hereinafter calledas an MR head, and there is a case in which an MR head of composite typeis simply called as an MR head) is used as a read head. Then, theseheads are structured in a composite form (a case of the layer structureas in the thin film type is included), thereby the composite head isstructured.

In consideration of the miniaturization of the future magnetic diskdrive and inclination of high density thereof, it is desirable thatthere is used a composite head wherein there is provided such a head issuperior to the conventional inductive head in sensitivity ofreproducing, the MR head whose reproducing output has no relation withthe relative speed of the head and the disk is used as a read head, andthe read head and the write head of the inductive type are structured ina composite form.

In a small-sized disk drive, a rotary actuator is used since thestructure is simpler than a linear actuator and there are advantages interms of low cost, excellent vibration resistance, and low consumptionof electric power, and so on (FIGS. 1A and 1B show one example of amagnetic disk drive of rotary actuator system).

The following explains a case in which the magnetic disk drive of therotary actuator system using the composite head in which the write headand the read head are structured in a composite form (for example, athin film magnetic head of composite type, which is structured bylayering a thin film magnetic head of inductive type, serving as a writehead, and MR head, serving as a read head). As shown in FIGS. 1A to 2,if the composite magnetic head is accessed in the range from aninnermost track position to an outermost track by rotating an arm of therotary actuator, misregistration is generated at a position of arecording track on the magnetic disk and a position of the read head bya skew angle θ. As shown in FIG. 2, an amount of track misregistrationcan be described by D·sinθ. D shows a space between a magnetic gap ofthe write head and that of the read head (FIG. 2 shows a case using theinductive head at both write and read operations, and central positionof a reproducing element effect section is meant in the case of the MRhead of FIGS. 1A and 1B, but hereinafter simply called as a magnetic gapas the similar meaning).

In the specification of the present invention, in order to visuallyeasily understand the relationship between the head position and themagnetic disk rotating direction, as shown in FIG. 2, an area where thewrite head traces is called as a recording track, and an area where theread traces is called as a reproducing track. In contrast, an area onthe magnetic disk for the recording/reproducing is originally performedis called a data track or simply as a track. In a case that the magneticdisk drive is structured in which the recording track and thereproducing track are conformed to each other when the positioning isperformed at the central track (in a case that the width of therecording track and that of the reproducing track are different, thecenters of both recording and reproducing tracks are conformed to eachother, and in a case that the centers of both tracks deviate, an amountof misregistration is shown by a distance between both centers), thepositional relationship between the recording track and reproducingtrack at each track position when the head is moved from the outermostcircumference to the innermost circumference, and an inclination of therecording/reproducing gap are shown in FIGS. 3A to 3C. FIGS. 3A to 3Cshow the inclination of the recording/reproducing gap, and the gaptherebetween is described wider than the actual case.

FIG. 4 shows an example of a format of the magnetic disk drive. At ahead of each sector, there is provided an ID section where IDinformation of the sector (cylinder number, head number, presence ornon-presence of defect depending, etc.) is recorded, it is needed thatID information be read before processing to a data area in any cases,that is, a case in which data is reproduced and a case in which data isrecorded.

A mode is changed in order that the write head is on a data track at awrite operation and the read head is on a data track at the writeoperation. In this case, if an offset amount of a voice coil motor (VCM)is finely adjusted so that a desired head flows the data track, the datasection can be recorded/reproduced without deteriorating S/N. However,since the ID section is required to be read at both read and writeoperations, the following problem occurs. More specifically, it isextremely difficult to change the mode such that the write head is setto be on track after reproducing the ID section physically existing inthe same sector by use of the reproducing head since the mode changemust be instantaneously performed.

If the width of the recording head is sufficiently made wider to thewidth of the read head, the reproducing track can be surely included inthe recording track. Due to this, ID information can be read withouthaving deterioration of quality of a signal of the data section causedby the writing/reading head misregistration. However, this is notfavorable in view of the point that a track density is increased.

"Track Density Constraints in the Application of MR Head Technology"IEEE TRANSACTION ON MAGNETICS, Vol. 28, No. 5, P. 2728, 1992 disclosesthe following two methods.

(1) The ID area and the data area are provided in a different physicalsector; and

(2) A plurality of ID (for reproducing and recording) is provided.

However, in the method (1), a through put of data access is lowered. Inthe method (2), though there is no description of the specificstructure, it is described that the ID area is divided into odd tracksand even tracks, and a plurality of ID is provided.

FIG. 5 is a view showing an example having a plurality of ID areas. FIG.6 is a view showing a method for recording a servo signal. According toFIG. 6, for example, servo information is written as shown by 1 to thefinal in accordance with head positions 1 to 5 at a servo writeoperation. Then, for example, the write head and the read head arecontrolled to be positioned to be at a center of the track at the writeand read operations, respectively. According to FIG. 5, there isprovided the structure in which each ID area to each track of the oddand even tracks is wider than the track, whereby ID information iscorrectly read. This structure is an effective method to solve the trackmisregistration. However, according to this method, since the servowrite does not conform to the ID area of each track (that is,information is overwritten with a half pitch of the read head), it isrequired that ID information be written twice, and it takes much time towrite ID information.

FIG. 7 is a view showing a general structure of the servo area.

Generally, the servo area has an address AGC area, an erased area, atrack address code area, a burst AGC area, a positioning data area, anda gap section. The address AGC area controls a gain of an auto gaincontrol (AGC) amplifier so as to standardize amplitude of a reproducedsignal, and ensures the detection of the sequential erased area and thereproduction of the track address code area. The erased area recognizesthe start of the servo area. An address in which the head exists isallotted to the track address code area. The burst AGC area adjusts thegain of the AGC amplifier so as to ensure extraction of positioninginformation from burst pattern data of the sequential positioning dataarea. The gap section absorbs of rotation jitter of the magnetic disk.

Generally, as shown in FIG. 8, the positioning data area of the harddisk drive in which the conventional inductive head is provided has aplurality of burst areas (in this example, A, B, C and D areas). In eachburst area, a burst signal area where continuous data is recorded withthe width Tp of the track pitch and an area erased in a DC manner arealternately provided in a direction of the width of the track. That is,the burst signal area and the erased area are provided as deviating inthe width direction of the track.

A dash and dotted line of FIG. 8 shows a center of each center. In orderto position the magnetic head at the center of the track, the positionof the magnetic head is controlled such that a value of (a-b)/(a+b) isset to 0 from amplitude a of the reproduced signal sent from the burstarea A and amplitude b of the reproduced signal sent from the burst areaB.

The burst areas C and D are recorded a position at which differs a halfpitch from the burst A and the burst B to obtain a good linearity evenin a case that the magnetic head is presented in an area where themagnetic head crosses the adjacent two tracks (i.e., in a case of headposition having wrong linearity obtained from position informationgenerated by the signals of the burst A and the burst B).

In order to form the above-mentioned positioning data area, as shown inFIGS. 9A to 9C, the recording of the positioning data area is performedby feeding the magnetic head by a half of the track pitch Tp, andoverwriting information on a base recording before the movement of thehead to a portion, and adjusting the phases.

In the case that the positioning data area is recorded by use of theinductive recording MR reproducing composite head (hereinafter, referredto as a composite MR head), there is known that an edge bipolar chargedirecting in a direction of the width of the track is generated at bothsides of the recording track. The similar phenomenon is generated when aDC erase is performed as shown FIG. 10A. FIG. 10B shows the structure ofthe write head section of the composite MR head. The magnetic gap isformed by a lower pole of the reproducing side and the upper pole oftrailing side. In reproduction using the composite MR head, if themagnetic flux sent from the edge bipolar charge is fetched to the MRfilm of the MR head, there is a problem in which offset is generated inthe reproduced signal in a DC manner.

According to the same method as the case using the conventionalinductive head, as shown in FIG. 11A, in a case that the edge bipolarcharge appears in the portion overwritten by the DC erase of positioningdata, and the edge bipolar charge is reproduced by the composite MR headso as to obtain head positioning information, since the MR head obtainsthe reproduced signal at the position where the MR head crosses the edgeof the burst area, the MR head is subjected to influence of the edgebipolar charge. Due to this, the reproduced signal of head positioninginformation has offset in the DC manner every burst area shown FIG. 11B.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a magnetic disk drivein which ID information can be stably read from a magnetic disk at writeand read operations with high reliability.

According to a first aspect of the present invention, there is provideda magnetic head drive comprising: a composite magnetic head structuredby integrally combining a write head into a record head; and a magneticdisk having a servo area where position information of the compositemagnetic head is recorded and a data area where data is recorded,wherein the servo area includes a positioning data area having headpositioning information, and the magnetic composite head has an erasedarea generated by recording an AC signal having a frequency higher thana burst pattern in an area other than The burst pattern includinginformation of positioning the composite magnetic head of thepositioning data area. Particularly, the magnetic disk drive of thepresent invention further comprises head tracking servo means forproviding a positioning offset to the composite magnetic head such thatthe write head is set to be on-track in the data area of the magneticdisk at a write operation and the read head is set to be on-track statein data area of the magnetic disk at a read operation.

According the first aspect of the present invention, in a case that aservo pattern is reproduced by use of an MR head is used, it is possibleto avoid generating offset in a DC form at a read operation of headpositioning information of head positioning data, thereby making itpossible to realize a correct positioning.

Moreover, according to the first aspect of the present invention, the ACsignal having a frequency higher than the burst pattern is recorded inan area, which is conventionally DC-erased, in positioning data, therebymaking it possible to prevent from appearance of an edge bipolar chargeand prevent from generation of DC-offset of the reproduced signal ofhead positioning information.

In the above-mentioned structure, the magnetic disk drive of the presentinvention further comprises a rotary actuator mounting the magnetic headon its one end and rotatable around another end, wherein the magneticdisk further includes first ID information recorded at a position wherethe read head is set to be on-track state at the data read operation andsecond ID information recorded at a position where the read head is setto be on-track state at the data write operation.

In order that the write head is set to be on-track in the data area atthe write operation and the read head is set to be on-track in the dataarea at the read operation, positioning offset is provided to themagnetic head. Also, there are provided first ID information recorded ata position where the read head is set to be on-track state at the dataread operation and second ID information recorded at a position wherethe read head is set to be on-track state at the data write operation.Whereby, since the ID section can be reproduced in a state that the readhead is on-track at any cases, information of the ID section can bestably read at both write and read operations.

Moreover, in the above-mentioned structure, the magnetic disk drivefurther comprises a rotary actuator mounting the magnetic head on itsone end and rotatable around other end, wherein the magnetic diskfurther includes an ID area having first ID information read by the readhead at the data read operation and second ID information, recorded at aformat different from the first ID information, read by the write headat the data write operation.

In order that the write head is set to be on-track in the data area atthe write operation and the read head is set to be on-track in the dataarea at the read operation, positioning offset is provided to themagnetic head. Also, first ID information, which is recorded by theformat suitable for reproducing by use of the read head, is read at thedata read operation in a state that the read head is on-track, andsecond ID information, which is recorded by the format suitable forreproducing by use of the write head, is read at the data writeoperation in a state that the write head is on-track. Whereby,information of the ID section can be stably read at both write and readoperations.

Furthermore, in the above-mentioned structure, the magnetic disk driveof the present invention further comprises a rotary actuator mountingthe composite magnetic head on its one end and rotatable around otherend, wherein the magnetic disk further includes an ID area recorded at arecording density different from the data area such that data is read bythe read head at the data read operation and data is read by the writehead at the data write operation.

In order that the write head is set to be on-track in the data area atthe write operation and the read head is set to be on-track in the dataarea at the read operation, positioning offset is provided to themagnetic head. Also, ID information, which is recorded with relativelylow record density as compared with the data area and can be read by anyof the read and write heads, is read by the read head at the readoperation in a state that the read head is on-track and by the writehead at the write operation in a state that the write head is on-track.Whereby, information of the ID section can be stably read at both writeand read operations.

According to a second aspect of the present invention, there is provideda magnetic disk drive comprising: a rotary actuator; a rotary actuatorarm having a first end mounting the composite magnetic head thereon anda second end connected to the rotary actuator; a composite magnetichead, mounted on other end of the rotary actuator arm, and structured byintegrally combining a write head into a read head; a magnetic diskhaving a servo area where positioning information of the compositemagnetic head is recorded and an ID area where ID information of asector is recorded, the ID area including a first ID area where aplurality of odd track ID areas are continuously formed and a second IDarea where a plurality of even track ID areas are continuously formed;and head tracking servo means for providing a positioning offset to thecomposite magnetic head such that the write head is set to be on-trackin the data area of the magnetic disk at a write operation and the readhead is set to be on-track state in data area of the magnetic disk at aread operation; wherein the servo tracking servo means includes meansfor setting a width of each of the odd track ID areas and that of eachof the even track ID areas to an integral multiple of a pitch width forservo positioning of the composite magnetic head recorded in the servoarea.

According to the second aspect of the present invention, the ID area isdivided into two areas of odd and even tracks, and the width of each ofthe ID area is set to an integral multiple of a pitch width of the servopositioning of the magnetic head. Due to this, since it is not neededthat ID information be overwritten with a half pitch of the write head,time for recording ID information can be shortened.

According to a third aspect of the present invention, there is provideda magnetic disk drive comprising: a rotary actuator; a rotary actuatorarm having a first end mounting the composite magnetic head thereon anda second end connected to the rotary actuator; a composite magnetichead, mounted on other end of the rotary actuator arm, and structured byintegrally combining a write head into a read head; a magnetic diskhaving an ID area where ID information of a sector is recorded; and headtracking servo means for providing a positioning offset to the compositemagnetic head such that the write head is set to be on-track in the dataarea of the magnetic disk at a write operation and the read head is setto be ontrack state in data area of the magnetic disk at a readoperation; wherein the ID area of the magnetic disk includes a first IDarea where an area recording ID information of an odd number track andan erased area erasing information are alternately recorded and a secondID area where an area recording ID information of the plurality of evennumber tracks and an erased area erasing information are alternatelyrecorded.

In the above third aspect of the present invention, positioning offsetis provided to the magnetic head in order that the write head is set tobe on-track in the data area at the write operation and the read head isset to be on-track in the data area at the read operation. Also, therecord positions of ID information on the odd number track and evennumber track are recorded based on the relation of the phase differentfrom each other, and both sides of the area where ID information isrecorded is an erased area. Due to this, a noise component cannot beread from the adjacent tracks even if the ID section is read at therecording mode in a state that the read head is on-track. Whereby,information of the ID section can be stably read at both write and readoperations.

According to a fourth aspect of the present invention, there is provideda magnetic disk drive comprising: a rotary actuator; a rotary actuatorarm having a first end mounting the composite magnetic head thereon anda second end connected to the rotary actuator; a composite magnetichead, mounted on other end of the rotary actuator arm, and structured byintegrally combining a write head into a read head; a magnetic diskhaving an area where cylinder number information is recorded, an areawhere sector number information is recorded, a servo area where servoinformation is recorded, and a data area where data is recorded; headtracking servo means for providing a positioning offset to the compositemagnetic head such that the write head is set to be on-track in the dataarea of the magnetic disk at a write operation and the read head is setto be on-track state in data area of the magnetic disk at a readoperation; and storing means for storing a defect sector of the magneticdisk and defect information of a defect track. At least one of thecylinder number information and sector number information is recordedwith a width equal to or larger than a track pitch. The cylinder numberinformation is recorded in a different phase each other in accordance iswith a remainder obtained when the cylinder number is divided by n (n: 2or more natural number). The magnetic disk has an area recording firstcylinder information recorded at a position where the read head ison-track at the read operation, second cylinder information recorded ata position where the read head is on-track at the data write operation,and sector number information recorded at a forward portion of each datasector with a width at least equal to or larger than a track pitch. Theread head reads the servo information, and the servo informationincludes first servo information recorded such that the write head isset to be on-track in the data area at the write operation, and secondservo information recorded such that the read head is set to be on-trackin the data area at the read operation.

According to the fourth aspect of the present invention, there isprovided head tracking servo means for positioning the magnetic headsuch that the write head is set to be on-track in the data area of themagnetic disk at a write operation and the read head is set to beon-track state in data area of magnetic disk at a read operation.Moreover, there is provided an area where cylinder number information isrecorded to be close to an area where servo information is recorded, sothat the cylinder number can be detected and confirmed. Furthermore,there is provided an area where sector number information is recorded atthe forward portion of each data sector, so that the sector number canbe confirmed before recording and reproducing.

Moreover, in order to store the defect sector on the disk and defecttrack information into a specific memory on the magnetic disk or anonvolatile solid memory, the defect sector and defect track informationare read at the time of staring the device, thereby making it possibleto confirm whether the sector to be accessed is a defect sector nor notbeforehand without accessing. The head number does not have to bewritten to the ID section if a physical head number and a logical headnumber are the same. In some magnetic disk drives, there is a case thatthe logical head number seen from the outer unit, the cylinder numberand the sector number are different from the logical head number, thecylinder number and the sector number, which are recorded on the disk.This case can be dealt by providing an allocation table is to a suitablememory. Therefore, the head number can be confirmed without recording itto the ID section. In other words, the ID section can be omitted.

In the above-mentioned structure of the first to fourth aspects of thepresent invention, in a case that there is used a magnetic disk in whichservo information for positioning the head including position errorinformation is recorded on a data surface, the following points can beprovided.

The magnetic disk alternately and dispersively records first servoinformation corresponding to the read head and second servo informationcorresponding to the write head, and the head tracking servo meansincludes means for positioning the composite magnetic disk based onposition information obtained by synthesizing first position informationobtained by cutting a low frequency component including a DC componentfrom first and second position error information showing position errorsof the read and write heads alternately obtained from first and secondservo information read from the magnetic disk by the head with secondposition information obtained by selecting first position errorinformation at the read operation and second position error informationat the recording time, respectively.

Discrimination information for discriminating whether servo informationis first servo information or second servo information is preferablyincluded in first and second servo information recorded in the magneticdisk.

If a sampling frequency is set to Fs and n is set to an integer number(0, 1, 2, . . . ), the above first position error signal is a signal inwhich a misregistration is generated by displacement of a complementaryangle in only the frequency of n·Fs/2, and an error is included. If n isan even number equal to or more than 2, since the frequency componentpasses through a Zero-order holding circuit and its output becomes azero output, the frequency component does not appear. Also, regardingthe frequency component wherein n is an odd number, since the level isreduced as n becomes larger due to a low pass filter characteristic ofthe Zero-order holding circuit, such a frequency component can beignored. However, the frequency component is Fs/2 when n=1, and thefrequency having such a frequency component cannot be ignored. Due tothis, first and second position error information is cut by the bandrejection filter of a narrow band frequency for cutting the component ofFs/2. The frequency of this filter is fixed, this filter has littleinfluence on other frequencies having a narrow band. In this case, n=0shows a direct current component. However, since an error is included inthe direct current component, a low frequency component including DCcomponent is cut from first and second position error information, andthe obtained information is used as first position information.

On the other hand, first and second position error information isrespectively selected in accordance with the reproducing or therecording, so that the selected information is used as second positionsignal. A sampling rate of second position information is Fs/2, and thefrequency band is a half of the band frequency of first positioninformation, but the band frequency is correct, and includes no error.However, since the band frequency of second position information isnarrow, phase distortion is generated in an area where the frequency ishigh. In order to avoid the generation of phase distortion, it ispreferable that only the low frequency portion is extracted through thelow pass filter.

The above obtained first position information including no DC componentand second position information having a small amount of AC componentare synthesized to form third position information, thereby obtainingsubstantially complete position information. The above-obtained thirdposition information has no component of Fs/2. However, since thirdposition information is substantially the same as position informationof the sampling rate Fs, the phase distortion is low up to the highfrequency. Therefore, the head tracking servo system for positioning thecomposite magnetic head is structured by use of the above-obtained thirdposition signal, whereby the trace of the read head is preciselyconformed to the that of the write head, so that there can be realizedthe magnetic disk drive in which the record tracks are arranged withhigh density.

In the structure of the first of fourth aspects of the presentinvention, the head tracking servo means preferably includes a bandrejection filter for cutting a frequency component of a 1/2 samplingrate from first position information. Also, head tracking servo meanspreferably includes a low pass filter for cutting a high frequencycomponent of second position information. Moreover, a Zero-order holdingcircuit for inputting position error information is preferably provided.

As mentioned above, according to the present invention, in the magneticdisk of the rotary actuator system on which the composite magnetic diskhaving the writing/reading heads in the composite form is mounted, sinceID information by the format improved to be suitable for the compositehead is provided, ID information can be surely read even if there ismisregistration in the recording track/reproducing track. Also, IDinformation can be surely read even if the read head is in an off-trackstate to the reproducing track at not only the read operation but alsothe write operation. Therefore, the record track density can be expectedto be largely improved as compared with the prior art.

Moreover, according to the present invention, in the magnetic disk ofthe rotary actuator system on which the composite magnetic disk havingthe writing/reading heads in the composite form is mounted, sincecylinder number information and sector number information by the formatimproved to be suitable for the composite head are provided, theseinformations can be surely read even if there is misregistration in therecording track/reproducing track. Also, these informations can besurely read even if the read head is in an off-track state to thereproducing track at not only the read operation but also the writeoperation. Therefore, the recording track density can be expected to belargely improved as compared with the prior art, and format efficiencyof data can be improved.

In addition, since a part of conditions necessary for confirming IDinformation can be written in recording servo information, there can beobtained an advantage in which the number of times of servo-diskformatting and the total sum of time can be reduced. This advantage isextremely helpful in realizing the high density magnetic disk drive onwhich the composite magnetic head is mounted.

Moreover, according to the present invention, in the magnetic disk ofthe rotary actuator system on which the composite magnetic disk havingthe writing/reading heads in the composite form is mounted, thecomposite magnetic head is positioned at a different position at each ofthe read and write operations, and the read head and the write head arepositioned at the same trace at the read and write operations. Whereby,there can be provided the magnetic disk drive with high record densitywithout narrowing an effective track width.

Additional objects and advantages of the present invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the present invention.The objects and advantages of the present invention may be realized andobtained by means of the instrumentalities and combinations particularlypointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe present invention and, together with the general description givenabove and the detailed description of the preferred embodiments givenbelow, serve to explain the principles of the present invention inwhich:

FIGS. 1A and 1B are views showing one example of a magnetic disk driveon which a rotary actuator is mounted;

FIG. 2 is a view for explaining a track misregistration based on a skewangle;

FIGS. 3A to 3C are views showing recording and reproducing trackmisregistrations at each track position;

FIG. 4 is a view showing one example of a magnetic disk format;

FIG. 5 is a view showing an example having a plurality of ID areas;

FIG. 6 is a view showing a recording method of a servo signal;

FIG. 7 is a view showing a general structure of a servo area;

FIG. 8 is a view showing a positioning data area of a hard disk drivehaving an inductive head;

FIGS. 9A to 9C are views showing a state where the positioning data areais formed;

FIGS. 10A and 10B are views showing a state where the positioning dataarea is recorded by use of a composite MR head;

FIGS. 11A and 11B are views explaining a defect of a DC erase;

FIGS. 12A to 12C are views showing a first embodiment of the presentinvention;

FIGS. 13A and 13B are views showing an ID section of the firstembodiment of the present invention;

FIGS. 14A to 14C are views showing a first modification of the firstembodiment of the present invention;

FIGS. 15A and 15B are views showing an ID section of the firstmodification of the first embodiment of the present invention;

FIGS. 16A to 16C are views showing a second modification of the firstembodiment of the present invention;

FIGS. 17A and 17B are views showing an ID section of the secondmodification of the first embodiment of the present invention;

FIG. 18 is an outline view of a magnetic disk drive of a secondembodiment of the present invention;

FIGS. 19A to 19C are views showing a first specific example of thesecond embodiment of the present invention;

FIGS. 20A and 20B are views showing the details of a cylinder number ofthe first specific example, and a sector number portion;

FIGS. 21A to 21C are views showing a second specific example of thesecond embodiment of the present invention;

FIGS. 22A and 22B are views showing a cylinder number portion of thesecond specific example of the second embodiment of the presentinvention;

FIGS. 23A to 23C are views showing a third specific example of thesecond embodiment of the present invention;

FIGS. 24A and 24B are showing a cylinder number portion of the thirdspecific example of the second embodiment of the present invention;

FIGS. 25A and 25B are views showing a third embodiment of the presentinvention;

FIG. 26 is a block diagram for recording a servo pattern of a fourthembodiment of the present invention;

FIG. 27 is a block diagram of a reproducing circuit in a case that theservo pattern of the fourth embodiment is used;

FIG. 28 shows one example of a recording pattern of a burst portion A ofthe present invention and that of a burst portion B;

FIGS. 29A to 29C are views showing a fifth embodiment of the presentinvention;

FIGS. 30A and 30B are views showing an ID section of the fifthembodiment of the present invention;

FIGS. 31A to 31C are views showing a sixth embodiment of the presentinvention;

FIGS. 32A and 32B are views showing an ID section of the sixthembodiment of the present invention;

FIGS. 33A to 33C are views showing a seventh embodiment of the presentinvention;

FIG. 34 are a view showing an ID section of the seventh embodiment ofthe present invention;

FIG. 35 is an arrangement plane of servo information on the magneticdisk of an eighth embodiment of the present invention;

FIG. 36 is a view showing the details of servo information of FIG. 35;

FIG. 37 is a block diagram showing the structure of a positioninformation generating circuit of the eighth embodiment of the presentinvention;

FIGS. 38A and 38B shows an example of equivalent magnetic field curvehaving recording magnetic field equal to coercivity (Hc) on the surfaceof the magnetic disk;

FIG. 39 is a schematic diagram for explaining a problem occurred duringrecording with single pole head (SPH) for a perpendicular recording;

FIGS. 40A to 40C show examples of improved ring heads;

FIGS. 41A to 41C show examples of improved single pole heads;

FIG. 42 shows an example of a trimmed Merged type MR composite head; and

FIG. 43 shows an example of a trimmed In-Gap type MR composite head.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be explained with reference tothe drawings.

A magnetic disk drive of a first embodiment of the present inventionwill be explained with reference to FIGS. 12A to 13B.

In a case that a composite magnetic head in which a write head and aread head are structured in a composite form is applied to a magneticdisk drive of a rotary actuator system, if the composite head is movedfrom an inner circumference to an outer circumference by a rotation ofthe rotary actuator, each of the write head W and the read head Rgenerates a positional misregistration at a respective track area asshown in FIGS. 12A to 12C.

In view of the design of the system, it is common to set the size of thetrack width and a guard band to a preferable relation. In this case, forsimplifying the explanation, track pitch, the write head and the writehead are drawn with the same width (the same in the following figures).In actual, as shown in FIGS. 3A to 3C, the head is inclined to a trackdirection (disk rotating direction). This is also omitted to simplifythe explanation (the same in the following figures).

FIGS. 12A to 12C show the positional relationship between an ID areaformat and the head in odd tracks of each of an outer circumferencesection, a center circumference section, and an inner circumferencesection. In order that the write head is set to be on-track in the dataarea of the magnetic disk at a write operation and the read head is setto be on-tack state in data area of the magnetic disk at a readoperation, a positioning offset is provided to the magnetic head,thereby making it possible to perform read/write operations in the dataarea. In this case, the read head reads information of an ID section inan off-track state at the recording mode. According to the presentinvention, since both sides of the ID section are an erased area, andthere is no case in which a noise component is read from the adjacenttracks. Therefore, according to the present invention, information ofthe ID section can be stably read at both write and read operations. Inthe present invention, since both sides of the ID section are erased,deterioration of quality of the signal of ID information is lenient in acase that the head is off-track by various types of noise anddisturbance. Due to this, the present invention has an advantage inwhich an off-track margin is larger than a conventional method in whichdata is recorded in the adjacent tracks.

FIGS. 13A and 13B show one example of a format of the ID section of thisembodiment together with a read gate signal of a controller forreproducing ID data. In this embodiment, since the recording positionsof ID information in odd number tracks and even number tracks arerecorded in a different phase relation, timing for reproducing IDinformation is changed at each of the odd tracks and the even tracks. AGAP 6 for changing various kinds of gate signals is provided asrequired. A width (W) recording ID information is equal to a recordwidth (Tp: the same as the track pitch since the guard band is omittedin this case) in the data area.

The both sides of the area where ID information is recorded is formed asan erased area. Then, regarding means for erasing, there can be suitablyselected a DC erase, an AC erase, etc. The AC erase is preferable asdescribed later. Easing may be performed at the time of formatting. Or,the front surface may be erased prior to the format. Or, in a case thata magnetic state of the magnetic disk before formatting is substantiallyequivalent to the erase state, recording may be performed based on theformat as shown in FIGS. 13A and 13B.

Twice area, which is used to write ID information, is needed. However,since the amount of data of the ID section is originally slight, thereduction of the format efficiency can be disregarded. Therefore, therecan be obtained an extremely large advantage in the improvement ofreliability and the density of the track.

A first modification of the magnetic disk drive of the first embodimentof the present invention will be explained with reference to FIGS. 14Ato 15B. In FIGS. 14A to 15B, the explanation of the portions common toFIGS. 12A to 13B is omitted.

In this modification, the positioning offset is provided to the magnetichead such that the write head is set to be on-track in the data area atthe write operation and the read head is set to be on-track in the dataarea at the read operation. Then, in order that the read head isincluded even when the read head is set to be in an off-track state atthe recording mode, the record width (W) of the ID section is made widerthan the record width (Tp) of the data section. Due to this, since theread head is always presented in the track in which ID information isrecorded, and reads ID information, information of the ID section can bestably read at both write and read operations.

In addition, similar to the first embodiment, since both sides of the IDsection are erased, there is brought about an advantage in which theoff-track margin is wide in the case that the head is off-track byvarious types of noise and disturbance.

Regarding the above-mentioned wide ID information area, for example, IDinformation is recorded with the same width as the data section, apredetermined amount of offset is added to the head, the phases arecorrectly arranged, and recorded ID information is overwritten to thepreviously written information, whereby, the above-mentioned wide IDinformation area can be obtained.

A second modification of the magnetic disk drive of the first embodimentof the present invention will be explained with reference to FIGS. 16Ato 17B. In FIGS. 16A to 17B, the explanation of the portions common toFIGS. 12A to 13B is omitted.

In this modification, the record width (W) of the ID section is the sameas the case of FIGS. 12A to 12C. However, a predetermined amount ofoffset (Δ) is added to the head at the ID information write operation soas to record ID information. The amount of offset (Δ) is fixed such thatID information is recorded at substantially the center between the readhead position at the write operation and the read head position at theread operation.

Similar to the above embodiment, the positioning offset is provided tothe magnetic head such that the write head is set to be on-track in thedata area at the write operation and the read head is set to be on-trackin the data area at the read operation. In this case, the provision ofthe positioning offset to the magnetic head is that the read head readsinformation in an off-track state, which is equal to the recording trackof ID information at both the write and read operations. Then, there isno generation in which either the write operation or the read operationis disadvantageous in terms of S/N, and as a general, reliability of thedevice can be improved.

Similar to the first embodiment, since both sides of the ID section areerased, there is brought about an advantage in which the off-trackmargin is wide in the case that the head is off-track by various typesof noise and disturbance.

FIG. 18 is an outline view of the magnetic disk drive of the secondembodiment of the present invention.

In this embodiment, there is used the magnetic disk 3 in which a servosignal for head positioning is recorded in the data surface. Thecomposite magnetic head 1 is attached to the rotary actuator 2. Themovement of the rotary actuator 2 is controlled in a radial direction ofthe magnetic disk 3 by a VCM (voice coil motor) 6 in accordance with atrack position control signal sent from a tracking servo circuit 12. Thetracking servo circuit 12 controls the positioning of the compositemagnetic head 1 in accordance with servo information reproduced througha recording/reproducing circuit 13, in order that the write head ison-track in the data area on the magnetic disk 3 at the write operation,and the read head is on-track in the data area at the read operation.

On the magnetic disk 3, there are provided an area where cylinder numberinformation is recorded, and an area where sector number information isrecorded. It is assumed that at least one of cylinder number informationand sector number information is recorded with a width larger than atrack pitch. The device of this embodiment has a defect informationstorage memory 15 comprising a nonvolatile solid memory for storing adefect sector on the magnetic disk 3 and defect track information. Thedefect sector on the magnetic disk 3 and defect track information may bestored in a specific area on the magnetic disk 3.

In the conventional magnetic disk drive, it is needed that IDinformation (cylinder number, head number, sector number, and presenceor non-presence of the defect) recorded in the head of each sectorshould be read before processing the data area even when the recordingor read operation is performed. In contrast, according to thisembodiment, since there is provided an area where cylinder numberinformation is recorded close to an area where servo information isrecorded, the cylinder number can be detected and confirmed. Then, sincethere is provided an area where sector number information is recorded inthe front of each data sector, it is possible to confirm the sectornumber before the recording or read operation.

Moreover, in the device of this embodiment, in order to store the defectsector on the disk and defect track information into the memory 10, thedefect sector and defect track information are read from the memory 10at the time of staring the device, thereby making it possible to confirmwhether the sector to be accessed is a defect sector nor not beforehandwithout accessing. The head number does not have to be written to the IDsection if a physical head number and a logical head number are thesame. In some magnetic disk drives, there is a case that the logicalhead number seen from the outer unit, the cylinder number and the sectornumber are different from the logical head number, the cylinder numberand the sector number, which are recorded on the disk. This case can bedealt by providing an allocation table is to a suitable memory.Therefore, the head number can be confirmed without recording it to theID section.

In this embodiment, it is needed that a hard disk controller 14 (HDC)for controlling the recording/producing circuit 13 be changed for theconventional HDC. However, processing can be performed by use of IDinformation (cylinder number, sector number, head number and detectinformation), which is sequentially confirmed by a different timing, bythe above-mentioned method in accordance with a condition of interface.In a case that the conventional IC for HDC, serving as HDC 14, is used,a suitable circuit is added thereto, and a signal may be transmitted bythe same timing when the conventional ID section is read before therecording/reproducing is performed in the data area.

According to the above-mentioned embodiment, even if a format in whichthe ID section is omitted is used in the magnetic disk 3, all necessaryID information can be confirmed prior to data write operation.

In recent years, the so-called sector servo system, which is popularlyused in a data surface servo system, has been mainly used in accordancewith improvement of track density. In a recording system at the sametransfer rate from the outer circumference to the inner circumference,the servo sector and the data sector are the same in almost all cases.In the case the both are the same, for example, servo data, cylindernumber information, and sector number information are sequentiallystored, and the data area continues after a suitable gap is provided forchanging the recording/reproducing circuit.

In contract, in so-called CDR (Constant Density Recording) system inwhich the data area is divided into several zones, the transfer rate isincreased in the outer circumference zone, and the recording isperformed at substantially the same recording density through the innerand outer circumferences so as to increase the capacity of data, thereis a case that both the servo sector and the data sector do not conformto each other. In such a case, cylinder number information is recordedsequentially after servo information of each servo sector, and sectornumber information is recorded in the head of each of the data sectorsthrough a suitable gap for changing the recording/reproducing circuit.

If the phases of sector number information are arranged (the phases arearranged in the zone in the case of CDR) and recorded, it isadvantageous that completely the same data can be read by therecording/reproducing track misregistration even if the head isoff-track.

Among the above ID information, cylinder number information and sectornumber information can be recorded at the same time at the servo writeoperation. In this way, by recording these cylinder number informationand sector number information at the same time at the servo informationwrite operation, the phases and the tracks can be correctly adjusted andrecorded similar to servo information. Unlike ID information recorded atthe time of the format in the prior art, high accurate recording inwhich the phase controlled can be performed. Moreover, time forrecording ID section at the formatting the disk can be omitted, andthere can be obtained an advantage in which a formatting efficiency canbe improved. The method for recording cylinder number information willbe explained in an embodiment described later.

As means for realizing the head tracking servo, which can position themagnetic head such that the write head is on-track in the data area atthe write operation and the read head is on-track in the data area atthe read operation, there may be used a servo pattern in which a headpositioning servo signal for is recording and a head positioning servosignal for reproducing are separately written. Or, in order tocompensate for the recording/reproducing track misregistration, offsetmay be provided to position the head. The following embodiment mainlydescribes a case in which the offset is provided.

A first specific example of the second embodiment will be explained withreference to FIGS. 19A to 20B.

As shown in FIG. 18, in a case that the composite head in which thewrite head and the read head are structured in the composite form isapplied to the magnetic disk drive on which the rotary actuator 2 ismounted, if the composite magnetic head 1 is moved from the inner trackof the magnetic disk 3 to the outer track of the magnetic disk 3 by therotation of the rotary actuator 2, as shown in the right side of each ofFIGS. 19A to 19C, each of the position of the write head (shown by W inthe figure) and the position of the read head (shown by R in the figure)generates a position misregistration in the track area.

If n is set to 2 or more natural number, cylinder number information isrecorded in a different phase relationship each other in accordance witha remainder obtained when the cylinder number is divided by n. Regardingthe setting the natural number, in consideration of therecording/reproducing track misregistration, head width tolerance, andamount of random off-track, if the width with which the read head canread information is set to X, n may be selected such that n TP>X(Tp=track pitch). In a case that the recording/reproducing trackmisregistration is small, n=1, that is, cylinder number information,which is recorded in the width of the full of the track pitch, is used.

FIGS. 19A to 19C show the case of n=2. That is, these figures show thepositional relationship between the cylinder number area format and thehead in the outer circumference section of the magnetic disk, centralsection, and odd tracks of the inner circumference section. Thepositioning offset is provided to the magnetic head such that the writehead is set to be on-track in the data area at the write operation andthe read head is set to be on-track in the data area at the readoperation, thereby making it possible to perform write/read operationsin the data area. In this case, the cylinder number section is read in astate that the read head is off-track at the time of the recording mode.However, since the cylinder number section has twice width as large asthe track pitch, there is brought about an advantage in which anoff-track margin is larger than a conventional method in which data arerecorded in the adjacent tracks.

FIGS. 20A and 20B show an example of the cylinder number section formatin this embodiment together with a read gate signal of a controller forreproducing the cylinder number section.

In this embodiment, since the recording positions of cylinder numberinformation in odd number tracks and even number tracks are recorded ina different phase relation each, timing for reproducing cylinder numberinformation is changed at each of the odd tracks and the even tracks. AGAP 6 for changing various kinds of gate signals is provided asrequired.

In the width (W) for recording cylinder number information, since thesame recording as the servo signal can be performed, the phases arearranged as information is sent in a radial direction with a half pitchof the track pitch, and overwritten, so that cylinder number informationis recorded in the width of the full of the track pitch. Therefore,cylinder number information can be recorded with a wider recording widththan the recording width of the data area (in the figures, since theguard band is omitted, the same width is shown), which is determined bythe width of the recording head. About twice area, which is used towrite cylinder number information, is needed. However, since the amountof data of the cylinder number area is originally slight, there can belarger advantage in the improvement of the format efficiency due to theomission of the ID section. Moreover, there can be obtained an extremelylarge advantage in the improvement of reliability and the track density.

FIGS. 21A to 22B show the positional relationship between a cylindernumber area format and the head in the track of each of the outercircumference section, center circumference section, and innercircumference section. In order that such that the write head is set tobe on-track in the data area at the write operation and the read head isset to be on-track in the data area at the read operation, thepositioning offset is provided to the magnetic head, thereby making itpossible to perform read/write operations in the data area. In thiscase, in order that the write head is set to be on-track state in thedata area at the write operation and the read head is set to be on-tackstate in the data area at the read operation, the positioning offset isprovided to the magnetic head. In addition, there are provided firstcylinder number information, which is recorded at a position where theread head is set to be on-tack state at the data read operation, andsecond cylinder information, which is recorded at a position where theread head is set to be on-track state at the data write operation. Dueto this, in any cases, the read head can reproduce the cylinder numbersection in a state that the read head is on-track, and cylinder numberinformation can be stably read at both write and read operations.

A third specific example of the second embodiment will be explained withreference to FIGS. 23A to 24B.

In this example, servo information is read by the read head so as torealize a head tracking servo, which can position the magnetic head suchthat the write head is set to be on-track in the data area at the writeoperation and the read head is set to be on-track in the data area atthe read operation. There are provided first servo information, which isrecorded such that the write head is set to be on-tack in the data areaat the write operation, and second servo information, which is recordedsuch that the read head is set to be on-track in the data area at theread operation. Thereby, the write/record heads can be correctly set tobe on-track at the recording/write operations, respectively.

A magnetic disk drive of a third embodiment of the present inventionwill be explained with reference to FIGS. 25A and 25B.

According to the third embodiment, the ID area is divided into two areasof odd and even tracks, and the width of each ID area is set to anintegral multiple of a pitch width of the servo positioning. In otherwords, as shown in FIG. 25A, the width of each of the ID areas is set betwice as large as the pitch width of the servo positioning. In thiscase, for example, the odd ID area has an width in which servopositioning pitches A and B are added. Thereby, since there is no needthat ID information is overwritten with a half pitch of the write head,time for recording ID information can be shortened.

A magnetic disk drive of a fourth embodiment of the present inventionwill be explained with reference to FIG. 26. FIG. 26 is a diagramshowing that a servo pattern is recorded in the present invention.

Prior to recording the servo pattern onto the magnetic disk 3, an index,serving as a reference and a clock for servo signal are written into thetrack (hereinafter called as a servo clock track), which is fixed on themagnetic disk 3, by use of a clock head 7 in order to record the servopattern generated by a clock generating circuit for separating indexsignal from servo signal. At the servo pattern write operation, theindex signal for obtaining timing to record the servo pattern and theclock for servo signal are reproduced by the clock head 7.

A clock separating circuit 27 for index and servo signals separates theclock for index and servo signals from a reproducing signal sent fromthe clock head 7, and transmits the signal to a servo pattern generatingcircuit 25. The servo pattern generating circuit 25 generates a signalfor recording the servo pattern based on timing due to the clock forindex and servo signals. At this time, burst pattern data in apositioning data area are generated based on the clock for servo signal.However, in an AC signal area other than the burst pattern ofpositioning data, the servo pattern is structured in accordance with theclock having a higher frequency than the frequency of the burst patterngenerated by a clock generating circuit 26 for AC signal. A series ofthe servo pattern recording signal, which is structured by the servopattern generating circuit 25, is sent to an recording/reproducingamplifier for the servo pattern recording, and recorded onto themagnetic disk 3 by the write head of the MR head.

The position of the head is detected by a head position detectingcircuit 23 using a laser measuring device. A head position controlcircuit 22 generates a head position control signal by use of a signalshowing the head position. An actuator driver 21 is driven, and theservo pattern is recorded as the head is sent. Thereby, a predeterminedservo pattern is recorded on the entire circumference of the magneticdisk.

FIG. 27 is a block diagram showing a generating circuit in a case thatthe servo pattern recorded by the device of FIG. 26 is used.

The reproducing signal reproduced by the MR head from the magnetic diskis amplified by a recording/reproducing amplifier, and sent to a servoarea/data area discriminating circuit 30, a data reproducing circuit 31,and a burst signal separating circuit 32. The reproducing signal, whichis recognized as a data area by the servo area/data area discriminatingcircuit 30, is modulated by the data reproducing circuit 31, andtransmitted as producing data. The reproducing signal, which isrecognized as a servo area by the servo area/data area discriminatingcircuit 30, is passed through a low pass filter or a bust signalseparating filter 31 having a band-pass filter characteristic,information is extracted from the bust pattern. Then, information issent to a servo circuit 33, and used in controlling the head position.

FIG. 28 is an example showing a recording pattern of a bust portion Aand that of a burst portion B. Similar to the burst portions A and B, inburst portions C and D, the portion other than the burst portions isrecorded by the AC signal having a higher recording frequency than theburst portions. The AC signal portion does not need to adjust to thephase every a half track pitch.

A fifth embodiment of the present invention will be explained withreference to FIGS. 29A to 30B. FIGS. 29A to 30B show the positionalrelationship between an ID area format and the head in the track of eachof the outer circumference section, center circumference section, andinner circumference section. In order that such that the write head isset to be on-track in the data area at the write operation and the readhead is set to be on-track in the data area at the read operation, thepositioning offset is provided to the magnetic head, thereby making itpossible to perform read/write operations in the data area.

According to this embodiment, there are provided first ID information,which is recorded at a position where the read head is set to beon-track at the read operation, and second ID information, which isrecorded at a position where the read head is set to be on-track in theat the write operation. Thereby, the read head reads the ID section in astate that the read head is on-track at the write/read operations, sothat information of the ID section can be stably read at both write andread operations.

FIGS. 30A and 30B show an example of the ID section format in thisembodiment together with a read gate signal of a controller forreproducing the ID section. In this embodiment, since the recordingposition of ID information is different in the write and readoperations, timing for reproducing ID information is changed at each ofthe write and read operations.

A sixth embodiment of the present invention will be explained withreference to FIGS. 31A to 32B. FIGS. 31A to 31C show the positionalrelationship between an ID area format and the head in the track of eachof the outer circumference section, center circumference section, andinner circumference section. In order that such that the write head isset to be on-track in the data area at the write operation and the readhead is set to be on-track in the data area at the read operation, thepositioning offset is provided to the magnetic head, thereby making itpossible to perform read/write operations in the data area.

According to this embodiment, at the data read operation, the read headreads first ID information, which is recorded by the format suitable forreproducing by use of the read head, in the on-track state. At the datawrite operation, the write head reads second ID information, which isrecorded by the format suitable for reproducing by use of the read headand different from first ID information, in the on-track state. Thereby,information of the ID section can be stably read at both write and readoperations.

In the composite head, the write head is naturally inferior to the readhead in the ability of reproduction. Due to this, it is needed thatsecond ID information read by the write head be by a suitable format forreproducing information in which a linear record density is made lowerthe first ID information for the head and redundancy is provided (forexample, strong ECC (error correction code)) by use of the write head.

FIGS. 32A and 32B show an example of the ID section format in thisembodiment together with a read gate signal of a controller forreproducing the ID section. In this embodiment, since the recordingposition of ID information is different in the write and readoperations, timing for reproducing ID information is changed at each ofthe write and read operations. Generally, since conditions such as thefrequency band of the filter and a constant of an equalizer aredifferent in the case that the signal is read by the read head and thecase that the signal is read by the write head, the reproducing circuitsystem or the constant of the circuit is preferably changed to besuitable for each case.

A seventh embodiment of the present invention will be explained withreference to FIGS. 33A to 33C, and 34. FIGS. 33A to 33C show thepositional relationship between an ID area format and the head in thetrack of each of the outer circumference section, center circumferencesection, and inner circumference section. In order that such that thewrite head is set to be on-track in the data area at the write operationand the read head is set to be on-track in the data area at the readoperation, the positioning offset is provided to the magnetic head,thereby making it possible to perform read/write operations in the dataarea.

According to this embodiment, ID information, which is recorded atrelatively low record density as compared with the data area and can beread even by the read head or the write head, can read by the read headin a state that the read head is in an on-track at the read operationand by the write head in a state that the write head is in an off-trackat the write operation. Due to this, information of the ID section canbe stably read at both write and read operations.

In the composite head, the write head is naturally inferior to the readhead in the ability of reproduction. Due to this, it is needed thatsecond ID information read by the write head be by a suitable format forreproducing information in which a linear record density is made lowerthe first ID information for the head and redundancy is provided (forexample, adding strong ECC (error correction code)) by use of the writehead.

FIG. 34 shows an example of the ID section format in this embodiment. Inthis embodiment, since common ID information is read at both write andread operations, it is unnecessary to change timing for reproducing IDinformation at the write and read operations. Generally, sinceconditions such as the frequency band of the filter and a constant of anequivalent circuit are different in the case that the signal is read bythe read head and the case that the signal is read by the write head,the reproducing circuit system or the constant of the circuit ispreferably changed to be suitable for each case.

FIG. 35 shows an enlarged view showing the arrangement of servoinformation on the magnetic disk of an eighth embodiment. In thisembodiment, first servo information 36 corresponding to the read headand second servo information 37 corresponding to the write head arealternately and dispersively recorded in a direction of a recordingtrack 35, that is, a disk rotating direction (shown by θ). Each of firstand second servo information 36 and 37 is used to position each of theread head and the write head.

FIG. 36 shows an enlarged view of servo information shown in FIG. 35. Inthis figure, there are formed a servo area where first and secondinformation for recording and reproducing position information arerecorded, and an ID section 1 and an ID section 2 for recording andrecording through a gap GAP. Since the ID section is normally read atboth write and read operations, two ID sections 1 and 2 are provided forrecording and reproducing. In the servo area, there is recordeddiscrimination information of 0 or 1 for discriminating whether servoinformation is first servo information (for recording) or second servoinformation (for reproducing). Discrimination information may beprovided in ether ID section 1 or ID section 2. However, discriminationinformation is preferably written in the servo area as mentioned aboveso as to prevent information of ID section 1 and ID section 2 from beingincreased.

Since the ID sections are dispersively recorded, the ID sections cannotbe read if the position of the track and that of the headmisregistrations. Due to these, two ID sections for recording andreproducing are used. Since servo information is written by a continuousrecording system, servo information can be read if the position of thetrack and that of the head misregistrations. Due to this, positioninformation for recording and reproducing appearing alternately can beread by one head.

FIG. 37 shows an example showing the structure of a position informationgenerating circuit, and showing the portions of therecording/reproducing circuit 13 of FIG. 18 and the tracking servocircuit 12, which are related to this embodiment.

The reproduced signal 30 is a signal, which is read from the magneticdisk of FIG. 36 by the read head, and includes first and second servoinformation. The reproduced signal 30 is inputted to a signal separatingcircuit 41. Then, position error information X, which includes first andsecond position error information obtained from first and second servoinformation by the well-known means, and a control signal C, whichincludes the discrimination signal for discriminating whether servoinformation is used for reproducing or recording, are separated fromeach other. In this case, first and second position error information isinformation showing the position error of each of the write head and theread head. A CPU 43 receives the control signal C from the signalseparating circuit 41, and controls the entire device.

Position error information C sent from the signal separating circuit 41is sampled with a sampling rate Fs (sampling frequency) by an A/Dconverter 42 including a Zero-order holding circuit, and converted to adigital signal. Thereafter, the digital signal is inputted to a bandrejection filter (BRF) 44, which cuts a frequency component of Fs/2.Then, a low frequency component including a DC component is cut by ahigh-pass filter (HPF) 45, so that first position information X1 isgenerated.

A selector 46 selects either first position error information, whichshows the position error of the read head, or second position errorinformation, which shows the position error of the write head, inaccordance with a select control signal generated by the CPU 43 based ondiscrimination information. Position error information selected by theselector 46 is inputted, and the high frequency portion whose phasecomponent is distorted is cut, so that second position information X2 isgenerated.

An adder circuit 48 adds and synthesizes first and second positioninformation X1 and X2, and outputs third position information X3. Inthis case, the cut-off frequency of the high-pass filter 45 and that ofthe low-pass filter 47 (low cut-off frequency and high cut-offfrequency) are conformed to each other, whereby first and secondposition information X1 and X2 are smoothly synthesized. Third positioninformation X3 is formed by synthesizing first position information X1including no DC component with second position information X2 havinglittle AC component. In third position information X3, there is nocomponent of Fs/2. However, third position information is substantiallythe same as position information of sampling rate Fs, and there islittle phase distortion up to the high frequency. Third positioninformation X3 is fed back to VCM 11 of FIG. 18 through a VCM driver(not shown), and positions the composite magnetic head 1 to apredetermined position.

The above embodiments explained the case of dealing with the trackmisregistration due to the skew angle. In addition, it is obvious thatthe following point can be performed by the embodiments of the presentinvention. More specifically, in order to deal with deterioration of thesignal generated by the recording/reproducing track misregistrationcaused by misregistration of the mask position during the step of layingthe write head and the head, offset is provided to the head inaccordance with misregistration of the write head and the read head andformatting is performed. The above-mentioned point is included in thefeature of the present invention.

A more preferably manner of write/read composite head for improving atrack density will be explained. In the following explanation, a portionof only the write head of the composite head will be illustrated andexplained except for in case of need.

FIGS. 38A and 38B are schematic diagrams for explaining a side fringingphenomenon occurred at write operation with a ring-type head. FIG. 38Ashows in case that skew angle is zero, FIG. 38B shows in a case that theskew is θ. A closed curve A shown in each of FIGS. 38A and 38B shows anexample of equivalent magnetic field curve having recording magneticfield equal to coercivity (Hc) on the surface of the magnetic disk.

It is common knowledge that magnetization of the magnetic disk isreversed by enlarging an intensity of the magnetic field of the headequal to or larger than Hc of the magnetic disk. Accordingly, an innerportion of the closed curve A is changeable area of the magnetizationand final recording state is basically determined by the magnetic fieldof the trailing edge of the head.

Since broad magnetic field is formed in a outside portion of the edgeopposite to the magnetic disk, a formed flux reversal becomes broad. Inaddition, it has a problem such that a reversal position is differentfrom the regular position and a noise of the magnetic disk is large.These phenomena are called as side fringing phenomenon in a general termand are important factors of narrowing an effective recording area,thereby obstructing an improvement of the track density.

When a recording is performed by using above-mentioned head, aninfluence of the side fringing is the same at right and left side of thehead (f_(R) =f_(L) =f₀) at which a skew angle is zero. When a skew angleis not zero, a width of trailed area by side fringing magnetic field iswidened and a normal recorded area is finally narrowed by the trailingedge at another edge. Therefore, an invalid area is extremely extended(f_(L) >f₀).

FIG. 39 is a schematic diagram for explaining a problem occurred duringrecording with single pole head (SPH) for a perpendicular recording. Theperpendicular recording with SPH having a feature that the side fringingeffect is extremely small than the in-plane recording with thering-head, since the magnetic field of the edge portion is rapidlyreduced.

The recording by the above-mentioned head having a skew angle has ademerit because of recording at side portion of the head. When a skewangle is not zero, a width of trailed area by side of the edge iswidened and a normal recorded area is not finally performed by thetrailing edge at another edge. Therefore, an invalid area is extremelyextended at read operation.

In order to solve the above problem, in the present invention, anarbitrary portion of the pole of the write head of the leading side ismade in a shape of the pole being in an area trailed by trailing edge ofthe write head on an arbitrary track from the innermost track to theoutermost track. The specific examples of the write head show in FIGS.40A to 43. It is assume that a skew angle at which the head positiondetermined at the outermost track is θ_(out) and a skew angle at whichthe head position is determined at the innermost track is θ_(in). Forconvenience, a sign of the angle is determined that θ_(out) is positivedirection and θ_(in) is negative direction, relatively.

FIGS. 40A to 40C show in some cases of ring head. In a case that one ofthe angle of the skew angle θ_(out) or θ_(in) is 0° or the same sign,one of the pole of the reading side may be trimmed. In a case that theskew angle is negative at inner circumference side and positive at outercircumference side, the head may be trimmed as shown in FIG. 40B. Thehead may be trimmed shown in FIG. 40C for the purpose of further lowingthe side fringing.

FIGS. 41A to 41C show in some cases of an SPH. In the SPH, which is sameas the ring head, in a case that one of the angle of the skew angleθ_(out) or θ_(in) is 0° or the same sign, one of the pole of the readingside may be trimmed. In a case that the skew angle is negative at innercircumference side and positive at outer circumference side, the headmay be trimmed as shown in FIG. 41B. The head can be trimmed shown inFIG. 41C to share up-faced head and down-faced head (|θ>|θ_(out) |,|θ_(in) |).

FIG. 42 shows an example of a trimming of a Merged type MR compositehead and FIG. 43 shows an example of a trimming of an In-Gap type MRcomposite head. In FIGS. 42 and 43, the various shapes can be employedaccording to the sign of skew angles θ_(out), θ_(in) and otherconditions same as FIGS. 40A to 40C.

The method of trimming is performed as follows. The composite head ismade in a normal process and a portion except for desired deletingportion deleted by trimming is masked by resist. The resist is removedafter trimming such as a method of etching or ion milling. A well-knownart such as FIB (Focused Ion Beam) processing can be employed as atrimming.

As described above, by using the above-mentioned write/read compositehead of the present invention, since an influence of such as sidefringing phenomenon can be suppressed in case of using the rotaryactuator, it is significantly effective to improve the track density.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the present invention in its broaderaspects is not limited to the specific details, representative devices,and illustrated examples shown and described herein. Accordingly,various modifications may be made without departing from the spirit orscope of the general inventive concept as defined by the appended claimsand their equivalents.

What is claimed is:
 1. A magnetic disk drive comprising:a rotaryactuator; a rotary actuator arm having a first end and a second endconnected to said rotary actuator; a composite magnetic head, mounted onsaid first end of said rotary actuator arm, and structured by integrallycombining a write head into a read head; a magnetic disk having an areawhere cylinder number information is recorded, an area where sectornumber information is recorded, a servo area where servo information isrecorded, and a data area where data is recorded; head tracking servomeans for providing a positioning offset to said composite magnetic headsuch that said write head is set to be on-track in the data area of saidmagnetic disk at a write operation and said read head is set to beon-track state in the data area of said magnetic disk at a readoperation; and storing means, including a nonvolatile solid-statememory, for storing defect sector information of said magnetic disk anddefect track information, wherein said magnetic disk further comprisesan area for recording first cylinder information, second cylinderinformation and sector number information, wherein the first cylinderinformation is recorded at a position where the read head is on-trackduring the read operation, wherein the second cylinder information isrecorded at a position where the write head is on-track during the datawrite operation, and wherein the sector number information is recordedat a forward portion of each data sector with a width at least as largeas a track pitch.
 2. A magnetic disk drive comprising,a rotary actuator;a rotary actuator arm having a first and a second end connected to saidrotary actuator; a composite magnetic head, mounted on said first end ofsaid rotary actuator arm, and structured by integrally combining a writehead into a read head; a magnetic disk having an area where cylindernumber information is recorded, an area where sector number informationis recorded, a servo area where servo information is recorded, and adata area where data is recorded; head tracking servo means forproviding a positioning offset to said composite magnetic head such thatsaid write head is set to be on-track in the data area of said magneticdisk at a write operation and said read head is set to be on-track statein the data area of said magnetic disk at a read operation; and storingmeans, including a nonvolatile solid-state memory, for storing defectsector information of said magnetic disk and defect track information,wherein said magnetic disk alternately and dispersively records firstservo information corresponding to said read head and second servoinformation corresponding to said write head, and said head trackingservo means includes means for positioning said composite magnetic diskbased on position information obtained by synthesizing first positioninformation obtained by cutting a low frequency component including a DCcomponent from first and second position error information showingposition errors of the read and write heads alternately obtained fromfirst and second servo information read from said magnetic disk by thehead with second position information obtained by selecting firstposition error information at the read operation and second positionerror information at the recording time, respectively.
 3. A driveaccording to claim 2, wherein discrimination information fordiscriminating whether servo information is first servo information orsecond servo information is preferably included in said first and secondservo information recorded in said magnetic disk.
 4. A drive accordingto claim 2, wherein said head tracking servo means further includes aband rejection filter for cutting a frequency component of a 1/2sampling rate from said first position information.
 5. A drive accordingto claim 2, wherein said head tracking servo means further includes alow pass filter for cutting a high frequency component of said secondposition information.
 6. A drive according to claim 2, furthercomprising a Zero-order holding circuit for inputting position errorinformation.
 7. A drive according to claim 2, whereina predeterminedportion of a write head pole of reading side of a trailing edge of awrite head of said composite magnetic head is situated with in a regionscanned by the trailing edge.
 8. A magnetic disk drive comprising,arotary actuator; a rotary actuator arm having a first and a second endconnected to said rotary actuator; a composite magnetic head, mounted onsaid first end of said rotary actuator arm, and structured by integrallycombining a write head into a read head; a magnetic disk having an areawhere cylinder number information is recorded, an area where sectornumber information is recorded, a servo area where servo information isrecorded, and a data area where data is recorded; head tracking servomeans for providing a positioning offset to said composite magnetic headsuch that said write head is set to be on-track in the data area of saidmagnetic disk at a write operation and said read head is set to beon-track state in the data area of said magnetic disk at a readoperation; and a nonvolatile solid-state memory for storing defectsector information of said magnetic disk and defect track information,wherein said magnetic disk alternately and dispersively records firstservo information corresponding to said read head and second servoinformation corresponding to said write head, and said head trackingservo means includes means for positioning said composite magnetic diskbased on position information obtained by synthesizing first positioninformation obtained by cutting a low frequency component including a DCcomponent from first and second position error information showingposition errors of the read and write heads alternately obtained fromfirst and second servo information read from said magnetic disk by thehead with second position information obtained by selecting firstposition error information at the read operation and second positionerror information at the recording time, respectively.